An earlier version of this story did not account for the fact that T-Mobile is waiving the $99 down payment on iPhones when people trade in their old devices. With this factored into the overall savings of the trade-in, T-Mobile's trade-in program actually offers consumers a better value than other trade-in sites such as Nextworth.

As part of its settlement with the Federal Trade Commission, T-Mobile will pay at least $90 million in customer refunds, as well as penalties and fines over complaints that it put bogus charges on customer bills.